1. Field of the Invention
This invention relates to an optical disk such as a CD and a DVD, and more particularly, to an optical disk having a non-true-circular contour.
2. Description of Related Art
As shown in FIG. 8, a conventional optical disk 1, which is generally used as a data-recording medium, has a true-circular contour. This kind of optical disk 1 has a ring-shaped clamping region. 3 having a central aperture 2, a wide ring-shaped data-recording region 4 provided outside the clamping region 3, and a very narrow transparent peripheral region 13 provided at the outermost peripheral edge of the disk, A reflection layer is provided to the optical disk 1 so as to correspond to the ring-shaped data-recording region 4.
On the other hand, Japanese Unexamined Laid-open Patent Publication NO. 5-012720 A discloses an optical disk having a cut-out portion in the outer periphery asymmetrically about a radial direction of between the top and reverse surfaces so that a visually handicapped person can easily recognize the top or reverse surface. However, since the cut-out portion is merely formed at the aforementioned very narrow outermost transparent peripheral region of the disk, the overall configuration of the disk is still recognized as a true-circular based shape, Furthermore, Japanese Unexamined Laid-open Patent Publication No. 10-269628 A (hereinafter referred to as JP"" 628) discloses an optical disk having a linear edge portion formed at a part of the peripheral region of the disk for easy positioning of a label. However, this optical disk also has a true-circular contour shape except for the linear edge portion and that the linear edge portion is formed at the very narrow outermost transparent peripheral region. Therefore, although a part of the outer peripheral edge is cut-out, the overall configuration of the disk is still recognized as a true-circular based shape, which fails to provide an effective designs.
In the meantime, JP"" 628 points out the following drawbacks regarding a non-circular optical disk: (1) Since a non-circular optical disk has a specific configuration, it becomes impossible to be taken out of a slot-in type car-stereo or a jukebox; (2) In a caddy type or a tray type player, a non-circular disk cannot be appropriately clamped, resulting in an unable reproduction of the data; and (3) Since a non-circular disk has an irregular weight balance, a heavy load may be imparted to a disk driver. Therefore, it cannot be used for a high-speed CD-ROM driver.
In considering the aforementioned drawbacks, JP"" 628 proposes that the reflection layer is provided so as to form a specific shape other than a true-circular shape irrespective of the circular reflection layer to enhance the design by the configuration of the reflection layer.
However, since this disk still has a true-circular based shape, the contour of the disk itself fails to provide any interesting design.
The present invention is made in view of the aforementioned technical drawbacks.
It is an object of the present invention to provide a practical optical disk which can be correctly clamped by a tray type disk driver although the disk has a non-true-circular shape.
According to one aspect of the present invention, a non-true-circular optical disk includes a disk substrate which internally touches a hypothetical true-circle corresponding to an outer periphery of a true-circular optical disk of a certain standard size. The disk substrate has a non-true-circular contour corresponding to a configuration shaped such that at least one cut-out portion is formed at an outer periphery of the hypothetical true-circle to thereby enhance a design. The disk substrate includes at least one inscribed outer peripheral edge internally touching the hypothetical true-circle. Furthermore, the aforementioned at least one inscribed outer peripheral edge includes a plurality of positioning points. The plurality of positioning points meet a geometrical positional relationship by which a rotational center of the disk substrate coincides with a center of the hypothetical true-circle and a movement of the rotational center relative to the center of the hypothetical true-circle is prevented in a state that the aforementioned at least one inscribed outer peripheral edge internally touches the hypothetical true-circle.
With this nun-true-circular optical disk, since the disk has a non-true-circular contour, the disk can provide an interesting design by the specific configuration of the non-true-circular contour which is different from that of a conventional trues circular or true-circular-based disk. Furthermore, even when a user places the non-true-circular disk onto a disk carrying tray having no positioning axis, the disk can be appropriately centered on the tray, resulting in an assured clamping of the disk by a disk driver.
If the aforementioned at least one cut-out portion is formed at an inside region beyond a narrow outermost transparent peripheral region with no reflection layer generally provided at a true-circular optical disk, the design effect can be further enhanced.
According to a second aspect of the present invention, the disk substrate includes three or more inscribed outer peripheral edges internally contacting the hypothetical true-circle, wherein the three or more inscribed outer peripheral edges include three or more positioning points, and wherein the three or more positioning points are positioned such that a total of a rotational-center-side interior angle of each triangle formed by segments connecting adjacent two positioning points and the rotational center becomes 360 degrees.
According to a third aspect of the present invention, the disk substrate includes three or more inscribed outer peripheral edges internally contacting the hypothetical circle, wherein the three or more inscribed outer peripheral edges include three or more positioning points, and wherein the three or more positioning points are positioned such that adjacent two positioning points are positioned on the hypothetical true-circle in a circumferential direction thereof at arcuate intervals each not exceeding a half circumference length of the hypothetical true-circle.
The aforementioned inscribed outer peripheral edge may inwardly contact the hypothetical true-circle at a point or in a line.